1. Field
Aspects of the present disclosure relate to crystal oscillators, and more particularly to method and system for dynamic gearshift during oscillation buildup by monitoring a duty cycle of an output of the crystal oscillator.
2. Background
Due to the inherent characteristics of certain crystals, they can be made to oscillate at a very precise frequency. Thus, crystal controlled oscillators are often used in applications where a precise frequency is required.
The crystal and its associated active circuitry together constitute a crystal oscillator. They form, in effect, a lossless inductor (L) capacitor (C) LC tank circuit that oscillates at a resonant frequency dictated by the values of the inductor and the capacitor.
Crystal oscillator circuits operate by virtue of positive feedback at or the near the resonant frequency of the crystal. The positive feedback is provided by an active circuit that poses, in effect, a negative impedance to the crystal. When power is initially applied to a crystal oscillator circuit, a large negative impedance effected by the active circuit overcomes the loss associated with the resistance (loss) of the crystal. As the amplitude builds up toward the final steady state at a frequency very close to the resonant frequency of the LC tank, the negative impedance created by the active circuit begins to diminish until it just matches the resistance of the crystal. Ultimately, it settles at precisely the resonant frequency of the LC tank. In other words, the loss encountered in the crystal is compensated for by the active circuit so that the oscillation can be sustained.
In some applications, the amount of time required to power up and stabilize an oscillator may be longer than desirable. Accordingly, for these applications it is desirable to reduce the time required to power up and stabilize the oscillator.